Vinyl chloride and vinylidene chloride polymers are known to be self-extinguishing and relatively more flame retardant than other polymers such as polyethylene, polypropylene and the like. However, a substantial amount of smoke may be produced upon exposure of vinyl chloride and vinylidene chloride polymers to a flame. The fact that an additive is a flame retardant does not necessarily mean that it will have good smoke retardant properties.
Inorganic and organometallic complexes of molybdenum are commercially useful as smoke suppressants in halogenated resins. Various amine molybdates have been investigated by B.F. Goodrich, see U.S. Pat. No. 4,153,792, for smoke suppression in PVC compounds. These compounds were plagued with poor performance properties due to residual molybdenum trioxide. The residual MoO3 causes blue discoloration of the resin systems coupled with poor thermal stability.
The most commercially recognized material for smoke suppression in PVC is ammonium octamolybdate (AOM). AOM is the premium material to make low smoke PVC compounds, particularly for plenum wire and cable applications. AOM is used in numerous PVC jacket formulations that pass the rigorous UL910 test for cables (cooper conductor and fiber optic cables).
U.S. Pat. No. 4,153,792 discloses the production of amine molybdates, especially melamine molybdate by reacting an amine, such as melamine, with molybdenum trioxide in an aqueous acidic medium under reflux.
U.S. Pat. No. 4,217,292 discloses the production of amine molybdates, preferably melamine molybdate by reacting an amine such as melamine with a stoichiometric quantity of molybdenum trioxide in an aqueous medium in the presence of an ammonium salt. The aqueous medium is essentially free of acid. The reaction may be conducted at temperatures within the range of 75-110xc2x0 C.
Organic salts of divalent copper are also well known as smoke suppressants for polyvinyl chloride resins. Most studies were done using copper (II) acetate or copper (II) formate. These materials were designed to undergo decomposition to ground state copper (Cuxc2x0). This is referred to as a reductive coupling mechanism. Reductive coupling results in significant reduction of smoke upon ignition due to char formation. Copper in its ground state is active in reductive coupling of halogenated resins. The difficulty with copper (II) salts are two fold.
1. The salts are blue or blue-green in color which also color the resin systems.
2. The salts upon decomposition cause instability of the halogenated resin by dechlorination without reductive coupling. This dechlorination accelerates decomposition to olefinic species.
The use of melamine molybdate and copper compounds such as copper acetate, copper oxalate, and copper formate as smoke suppressants in halogenated resins, particularly PVC is well known. This technology was never commercialized due to the technical failures of these systems. The pitfalls include:
Blue to green discoloration of the resin systems,
Poor thermal stability of the compounded resin systems, and
Loss of fire resistance characteristics due to the thermal instability of the compounded resin systems.
According to this invention, there is provided a method of improving the smoke suppressant characteristics of halogen-containing polymeric compositions which comprises adding to said polymeric compositions a smoke retardant amount of (1) a complex of a cuprous halide and a phosphite, and (2) an amine molybdate which contains no residual molybdenum trioxide prepared by reacting an amine, preferably melamine, with molybdenum trioxide in an aqueous acidic medium under greater than atmospheric pressure and at a temperature of from 105-150xc2x0 C. The reaction between the molybdenum trioxide and amine is conducted for a time sufficient to eliminate all detectable amounts of molybdenum trioxide. As win be seen hereinafter, several of the combinations of a complex of a cuprous halide and a phosphite, and an amine molybdate provide a synergistic action, ie., the smoke suppressant results are greater than the additive effect of the two materials being used separately.
The copper complex is prepared by mixing 1 mole of phosphite with 0.01 mole to 1.0 mole of cuprous halide, preferably cuprous bromide or cuprous chloride, and most preferably cuprous chloride. The materials are mixed at 80xc2x0 C. in an inert atmosphere (e.g., nitrogen) until the cuprous halide is dissolved. If the phosphite is a liquid, no additional solvent is required. However, if the phosphite is not a liquid, the reaction may be conducted in any non-reactive solvent, such as benzene, toluene or xylene. The dissolution time is typically 5 to 8 hours. The reaction mass is filtered with filter aid (e.g., diatomaceous earth, celatom FW-12, celite, etc.) under an inert atmosphere to yield a clear and colorless liquid. An exception is the reaction product of triphenylphosphite with cuprous chloride which yields a white crystalline solid melting at 65xc2x0 C.
The phosphite may be any commercially available phosphite such as tris-dodecyl phosphite, tris-tridecyl phosphite, tris-C12-15 alkyl phosphite, tetraphenyl dipropylene glycol diphosphite, poly(dipropylene glycol)phenyl phosphite, alkyl(C12-15)bisphenol A phosphite, alkyl(C10)bisphenol A phosphite, distearyl pentaerythritol diphosphite, trisnonylphenyl phosphite, triisooctyl phosphite, diisodecyl pentaerythritol diphosphite, heptakis(dipropylene glycol)triphosphite, poly-4,4xe2x80x2-isopropylidenediphenol C12-15 alcohol phosphite, tris-dipropyleneglycol phosphite, poly(dipropylene glycol)phenyl phosphite, diphenyl isooctyl phosphite, tris(2,4-t-butylphenyl)phosphite, bis(2,4-dicumylphenyl) pentaerythritol diphosphite, tris butoxyethyl phosphite, triphenyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite and diphenyl phosphite.